[codex] fix Windows ConPTY input handling (#29734)

## Why

Windows unified-exec TTY input did not behave like the non-Windows PTY
path. ConPTY sessions could receive the wrong line ending or mishandle
backspace, especially when sending input to a foreground program through
PowerShell or cmd. The local, legacy restricted, and elevated paths also
handled this normalization separately.

## What changed

- share one stateful Windows TTY input normalizer across local, legacy
restricted, and elevated runner paths
- translate LF and split CRLF into one Windows terminal Enter, encode
backspace as DEL, and preserve UTF-8 and control bytes such as Ctrl-C
- add Windows integration coverage for Unicode input, backspace, Enter,
and PowerShell foreground-child Ctrl-C behavior

## Validation

- `just test -p codex-utils-pty` (13 tests passed; the Unicode
integration test retried once)
- the Unicode integration test passed five consecutive runs with retries
disabled
- integration coverage sends `cafeé 漢字` through cmd and PowerShell and
verifies that Ctrl-C interrupts a running PowerShell foreground child

codex-rs/windows-sandbox-rs/src/unified_exec/backends/legacy.rs

@@ -1,5 +1,4 @@
 use super::windows_common::finish_driver_spawn;
-use super::windows_common::normalize_windows_tty_input;
 use crate::conpty::ConptyInstance;
 use crate::conpty::spawn_conpty_process_as_user;
 use crate::desktop::LaunchDesktop;
@@ -22,6 +21,7 @@ use codex_utils_absolute_path::AbsolutePathBuf;
 use codex_utils_pty::ProcessDriver;
 use codex_utils_pty::SpawnedProcess;
 use codex_utils_pty::TerminalSize;
+use codex_utils_pty::WindowsTtyInputNormalizer;
 use std::collections::HashMap;
 use std::path::Path;
 use std::ptr;
@@ -153,13 +153,13 @@ fn spawn_input_writer(
     normalize_newlines: bool,
 ) -> tokio::task::JoinHandle<()> {
     tokio::task::spawn_blocking(move || {
-        let mut previous_was_cr = false;
+        let mut windows_input = WindowsTtyInputNormalizer::default();
         while let Some(bytes) = writer_rx.blocking_recv() {
             let Some(handle) = input_write else {
                 continue;
             };
             let bytes = if normalize_newlines {
-                normalize_windows_tty_input(&bytes, &mut previous_was_cr)
+                windows_input.normalize(&bytes)
             } else {
                 bytes
             };

codex-rs/windows-sandbox-rs/src/unified_exec/backends/windows_common.rs

@@ -11,6 +11,7 @@ use anyhow::Result;
 use codex_utils_pty::ProcessDriver;
 use codex_utils_pty::SpawnedProcess;
 use codex_utils_pty::TerminalSize;
+use codex_utils_pty::WindowsTtyInputNormalizer;
 use codex_utils_pty::spawn_from_driver;
 use std::fs::File;
 use tokio::sync::broadcast;
@@ -25,23 +26,6 @@ pub(crate) fn finish_driver_spawn(driver: ProcessDriver, stdin_open: bool) -> Sp
     spawned
 }
 
-pub(crate) fn normalize_windows_tty_input(bytes: &[u8], previous_was_cr: &mut bool) -> Vec<u8> {
-    let mut normalized = Vec::with_capacity(bytes.len());
-    for &byte in bytes {
-        if byte == b'\n' {
-            if !*previous_was_cr {
-                normalized.push(b'\r');
-            }
-            normalized.push(b'\n');
-            *previous_was_cr = false;
-        } else {
-            normalized.push(byte);
-            *previous_was_cr = byte == b'\r';
-        }
-    }
-    normalized
-}
-
 pub(crate) fn start_runner_pipe_writer(
     mut pipe_write: File,
 ) -> std::sync::mpsc::Sender<FramedMessage> {
@@ -63,10 +47,10 @@ pub(crate) fn start_runner_stdin_writer(
     stdin_open: bool,
 ) -> tokio::task::JoinHandle<()> {
     tokio::task::spawn_blocking(move || {
-        let mut previous_was_cr = false;
+        let mut windows_input = WindowsTtyInputNormalizer::default();
         while let Some(bytes) = writer_rx.blocking_recv() {
             let bytes = if normalize_newlines {
-                normalize_windows_tty_input(&bytes, &mut previous_was_cr)
+                windows_input.normalize(&bytes)
             } else {
                 bytes
             };